We’ve been going over some basic quilty math and we’re up to Part 4.

We’ve seen how helpful it is to think of a block in sections or columns.

This block is divided into four sections or columns. If you know it’s a 12″ block, you can determine the width of each section like this:

12″ ÷ 4 = 3″

Each section finishes at 3 inches wide. But I said we’d talk about that center blue patch. It’s bigger than one section, OH NO! Not to worry—we can figure it out. We know that each section is 3″. The blue patch covers 2 sections. So we figure it like this:

3″ x 2 = 6″

The next thing I want to mention is half-square triangles. Earlier in the series we talked about the 7/8″ rule: For half-square triangles (also called triangle-squares), you take the finished size and add 7/8″, then cut in half diagonally.

If the block above was a 15″ block, you’d know that 15″ divided by 5 sections makes each section 3″ wide. So you want that half-square triangle (outlined in black) to finish at 3″. Add 7/8″ and you know to cut squares 3 7/8″, cut them in half diagonally and sew them together (with a patch of the same size in a different color, as shown), and you’ll get a square that’s 3.5″, to finish at 3″.

But sometimes sewing across that wobbly bias is troublesome, right? The good news is that there are other ways to do it.

The simplest variation is to cut squares from two different fabrics, both 3 7/8″ x 3 7/8″. On the wrong side of the fabric, draw a diagonal line across one of the squares.

The stitching 1/4" out from one side of the drawn line is complete. The stitching on the other side is being sewn.

Place the squares right sides together. Sew 1/4″ out from the drawn line on each side as shown in the photo above. Cut on the drawn line and press the triangle-squares open. This yields 2 triangle-squares.

Cut on the marked line with a rotary cutter or a scissors.

When you press these open, you’ll see that the little triangle tips, or “dog-ears” are there. Most people trim them off.

The little triangular "dog-ears" may be trimmed off.

Some people prefer a different approach. They choose to cut their squares a bit larger and then trim the triangle-squares down. Creative Editor Carolyn Beam prefers this method. For 3″ finished, Carolyn would just cut 4″ squares and make her HSTs (that’s quiltspeak for Half-Square Triangles). After pressing the HSTs open, she trims them to 3 1/2″.

One of my favorite tools is the Easy Angle ruler. Instead of adding 7/8″ to the finished size, you add 1/2″ to the finished size. In our example, you’d cut 3 1/2″ strips and then use the Easy Angle to cut the triangles from these strips, as shown below. It’s a very simple concept and the ruler is easy to use. See Simplicity’s instructions for the Easy Angle. Bonnie Hunter of Quiltville fame is a big fan of the Easy Angle. (See Bonnie use it on My Blue Heaven.)

Using the Easy Angle ruler to cut HSTs from strips; notice that the top set of dog-ears isn't there.

Look at the photo below. Inside the black box I’ve drawn, you’ll see that there are no dog-ears. With the Easy Angle, you don’t have to allow for those little dog-ears, also called “bunny ears” or triangle tips.

No dog-ears!

They amount to a difference of 3/8″—which is the difference between 3 1/2″ (the size for Easy Angle) and 3 7/8″ (the size for other methods). Even if this is clear as mud, do give the Easy Angle ruler a try. It’s inexpensive and I think you’ll like it.

Part 5 soon to come!

About Diane Harris

I'm an editor for Quiltmaker magazine in Golden, Colorado, USA. For six years, I wrote pattern instructions, product reviews and how-to articles. Then I spent four years as QM's Interactive Editor, working to generate much of our online content. Now I'm back to patterns and how-tos, which is a great fit for me. I still love writing about quilt-related topics for Quilty Pleasures, and I always have my finger on the pulse of the quilting world. I teach a variety of quilt classes and give guild programs, too. Reach me by email: editor@quiltmaker.com.

Hi there, great article! This is just what my friend and I needed for our classes challenge, so appreciate it quite definitely.
My friend and I don’t usually comment although this is a real comfort that I couldn’t resist.

I MUCH prefer using the Easy Angle ruler – less fabric wastage (is that a word?) – that stuff is expensive and why cut more than you need and then cut it down and throw it away? As my country cousin would say “that don’t make a lick o’ sense!”